Seal assembly and method of manufacturing the same

ABSTRACT

A seal assembly and method for the manufacture thereof is provided. The seal assembly provides a dynamic fluid seal between a housing having a bore and a shaft having an outer running surface rotating within the bore. The seal assembly comprises a rigid carrier for supporting the seal assembly within the bore of the housing. A flexible member is mounted to the rigid carrier. The flexible member is formed from an elastomeric material that allows the flexible member to flex during use. A sealing element is retained by the flexible member about the outer running surface. The sealing element is formed from a non-polytetrafluoroethylene bearing grade plastic material having a hardness relatively greater than a hardness of the elastomeric material of the flexible member. The sealing element moves with the flexible member as the flexible member flexes. The sealing element extends along the outer running surface in a plurality of helically wound convolutions.

FIELD OF THE INVENTION

The present invention relates generally to seal assemblies used toprovide a dynamic fluid seal between a housing and a shaft having anouter running surface rotating relative to the housing. Morespecifically, the present invention relates to sealing elements used insuch seal assemblies, including the materials and shapes used to formsuch sealing elements, and the method for manufacturing such sealingelements.

BACKGROUND OF THE INVENTION

Seal assemblies are well known for providing a dynamic fluid sealbetween a housing having a bore and a shaft having an outer runningsurface protruding through the bore and rotating relative to thehousing. Such seal assemblies typically comprise a rigid carrier forsupporting the seal assembly in the bore. A mounting collar formed fromrubber is often molded about the rigid carrier to provide a press-fitconnection between the seal assembly and the housing thereby aligningthe seal assembly within the bore about the outer running surface. Therigid carrier supports a sealing element, e.g., a lip seal, encirclingand dynamically sealing the outer running surface of the shaft.

The sealing element, e.g., the lip seal, is often formed frompolytetrafluoroethylene (PTFE) because PTFE offers superior thermal andchemical resistance and a low coefficient of friction. However, PTFE hascomparatively low wear and abrasion resistance and is costly, limitingits use to only certain sealing applications or requiring extra measuresto protect the PTFE from damage from the environment.

It is an object of the present invention to provide a seal assemblywhich overcomes or minimizes the drawbacks to typical PTFE seals, whilepreserving their advantages.

BRIEF SUMMARY OF THE INVENTION AND ADVANTAGES

A seal assembly constructed according to a first aspect of the inventionis operative to provide a dynamic fluid seal between a housing having abore and a shaft having an outer running surface rotating within thebore. The outer running surface rotates about an operational axisrelative to the housing. The seal assembly includes a rigid carrier forsupporting the seal assembly within the bore of the housing and aboutthe outer running surface. A flexible member of elastomeric material ismounted to the rigid carrier. The flexible member flexibly retains asealing element in sealing relation with the outer running surface asthe outer running surface rotates about the operational axis. Thesealing element is formed from a non-polytetrafluoroethylene (non-PTFE)bearing grade plastic material. The non-PTFE material has a hardnessthat is relatively greater than a hardness of the elastomeric materialof the flexible member.

One advantage of this seal assembly is the ability to use non-PTFEbearing grade plastic material for the sealing element. This provides asubstantial cost savings over traditional materials such as PTFE, whileproviding a higher wear and abrasion resistant material suitable fordynamic fluid sealing. Traditionally, such materials have not been usedfor sealing elements given the rigid nature of such materials, i.e., asthe shaft becomes misaligned in the bore the sealing element wearsunevenly thus deteriorating the sealing relation with the shaft. Withthe seal assembly of the present invention, the flexible member is ableto flex as the shaft becomes misaligned in the bore. Thus, the sealingelement, which is retained by the flexible member, can be less flexible,since the sealing element moves with the flexible member.

In another aspect of the present invention, the sealing element extendsin a plurality of helically wound convolutions about the outer runningsurface. The convolutions provide a hydrodynamic effect which acts as apump to redirect any fluid that finds its way under the seal back towardthe interior (“oil side”) of the seal. The convolutions can be single ormultiple start thread form, and can be uni or bi-directional, ifdesired.

The present invention further provides a method of manufacturing a sealassembly with the plurality of helically wound convolutions. The methodincludes forming a groove extending helically within a surface of astock piece of sealing material to define a fracture line within thestock piece. The stock piece is then fractured along the fracture lineto form the sealing element. By forming the groove to define thefracture line, the method of manufacturing the seal assembly provides asimple and cost effective procedure for forming the sealing element withthe plurality of convolutions.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

These advantages and features of the present invention will be readilyappreciated as the same becomes better understood by reference to thefollowing detailed description when considered in connection with theaccompanying drawings wherein:

FIG. 1 is a fragmentary cross-sectional view of a seal assemblyaccording to the present invention;

FIG. 2 is a fragmentary cross-sectional view of the seal assemblyillustrating misalignment of a shaft rotating about an operational axis;

FIG. 3 is a perspective view of a sealing element of the seal assembly;

FIG. 4 is a perspective view of an alternative sealing element of theseal assembly;

FIG. 5 is a fragmentary cross-sectional view of the sealing element ofthe seal assembly according to an alternative embodiment of the presentinvention;

FIG. 5A is a fragmentary cross-sectional view of a cylindrical stockpiece of non-PTFE material used to form the sealing element shown inFIG. 5;

FIG. 6 is a fragmentary cross-sectional view of the sealing element ofthe seal assembly according to an alternative embodiment of the presentinvention; and

FIG. 6A is a fragmentary cross-sectional view of a cylindrical stockpiece of non-PTFE material used to form the sealing element shown inFIG. 6.

DETAILED DESCRIPTION OF THE INVENTION

Referring to the Figures, wherein like numerals indicate like orcorresponding parts throughout the several views, a seal assembly of thepresent invention is generally shown at 10. The seal assembly 10 is wellsuited for a multitude of applications in which a dynamic fluid seal isrequired. Such applications may include automotive and industrialapplications. The seal assembly 10 is illustrated herein for use in ashaft seal system 11.

With reference to FIG. 1, the shaft seal system 11 uses the sealassembly 10 to provide a dynamic fluid seal between a housing 12 havinga bore 14 and a shaft 16 having an outer running surface 15 rotatingwithin the bore 14. The outer running surface 15 rotates about anoperational axis A relative to the housing 12. In FIG. 1, the outerrunning surface 15 is presented by an annular wear sleeve 28 that ispress fit to the shaft 16. The wear sleeve 28 is press fitted to theshaft 16 for purposes well-known to those skilled in the art, such as toprovide a manufactured running surface. As will also be appreciated bythose skilled in the art, the present invention could be practicedwithout the wear sleeve 28. The wear sleeve 28 rotates with the shaft 16in the bore 14. The bore 14 of the housing 12 is formed with acylindrical stepped bore wall 17 disposed about the shaft 16 and anannular axially facing shoulder 19 disposed transverse to the bore wall17.

A carrier 18 supports the seal assembly 10 in the bore 14. The carrier18 includes a U-shaped base portion 20 and an annular flange 22extending radially inwardly from an end of the base portion 20. Thecarrier 18 is preferably formed from a rigid material such as metal. Anelastomeric mounting collar 24 is formed annularly about the rigidcarrier 18 to press fit the seal assembly 10 into the bore 14 therebyproviding a barrier to retain the fluid within the housing 12. Theelastomeric mounting collar 24 presses against the bore wall 17 and theshoulder 19 to provide the press fit. A retainer ring 32 may be seatedwithin a similarly shaped pocket 34 in the housing 12 to secure the sealassembly 10 within the bore 14.

An annular baffle 30 may be fixed to the wear sleeve 28 and positionedwithin an annular chamber defined by the U-shaped base portion 20 of therigid carrier 18 to define a labyrinth path for inhibiting the ingressof dirt and debris into the seal. A filter 26 may be disposed within thelabyrinth and mounted to the carrier 20 or wear sleeve 28, if desired,to further assist in entrapping the dirt and debris. When the filter 26is mounted to the carrier 20, the wear sleeve 28 and annular baffle 30rotate relative to the filter 26 as the shaft 16 rotates about theoperational axis A.

A flexible member 36 of elastomeric material is mounted to and suspendedfrom the rigid carrier 18. The elastomeric material has a hardness ofsuch a magnitude that the flexible member 36 is capable of flexureduring use, while maintaining shape, e.g., a Shore A hardness of 25-75or a Shore D hardness of less than 50. The elastomeric material mayinclude rubber or other like materials.

The flexible member 36 includes a longitudinal portion 39 lyinggenerally parallel to the operational axis A. First 40 and second 42annular lips project radially outwardly from the longitudinal portion 39to define a notch 44 therebetween for receiving the annular flange 22 ofthe rigid carrier 18. This sealably secures the flexible member 36 tothe annular flange 22. The flexible member 36 also includes third 46 andfourth 48 lips projecting radially inwardly from the longitudinalportion 39. A gap may be maintained between each of the third 46 andfourth 48 lips and the outer running surface 15.

The flexible member 36 flexibly retains a radially acting sealingelement 38 about the outer running surface 15. In the preferredembodiment, the flexible member 36 is molded to the sealing element 38.The flexible member 36 acts as an annular hinge 36 between the annularflange 22 of the rigid carrier 18 and the sealing element 38. Thesealing element 38 includes an exterior surface 50 in frictional moldedcontact with the flexible member 36 to retain the sealing element 38against the flexible member 36. In other embodiments, the exteriorsurface 50 is chemically bonded to the flexible member 36. The sealingelement 38 further includes a radially inner annular sealing surface 52extending axially along the outer running surface 15 in sealing relationtherewith. At the same time, the third lip 46 of the flexible member 36abuts the sealing element 38 to retain the sealing element 38 frommoving axially in one direction.

Referring to FIG. 2, the sealing element 38 moves with the flexiblemember 36 as the flexible member 36 flexes relative to the rigid carrier18 when the shaft 16 becomes radially misaligned (shown greatlyexaggerated) relative to the rigid carrier 18. At the same time, theradially inner annular sealing surface 52 maintains the sealing relationwith the outer running surface 15. Thus, the flexible member 36 acts asa flexible extension of the sealing element 38 allowing the radiallyinner annular sealing surface 52 to maintain the sealing relation withthe outer running surface 15 even when the shaft 16 experiences a runoutcondition or other misalignment condition within the bore 14.

The sealing element 38 is formed from a non-polytetrafluoroethylene(non-PTFE) bearing grade plastic material. It should be appreciated thatthe non-PTFE material may contain some PTFE filler, but at levels ofless than fifty percent by weight or volume. The non-PTFE material ispreferably a thermoplastic material having a hardness relatively greaterthan the hardness of the elastomeric material forming the flexiblemember 36. Hence, the sealing element 38 is more rigid than the flexiblemember 36. The non-PTFE material exhibits a tensile strength greaterthan five thousand pounds per square inch and a compressive strengthgreater than five thousand pounds per square inch (using ASTM D638 tomeasure tensile strength and ASTM D695 to measure compressive strength).Additionally, the non-PTFE material has a wear factor “k” of less than200×10⁻¹⁰ in.³-min/ft.lbs.hr.

The non-PTFE material used to form the sealing element 38 may includeany imidized, semi-crystalline, or amorphous bearing gradethermoplastics such as nylon, acetal, polyethylene terepthalate (PET-P),polyetheretherketone (PEEK), polyphenylene sulfide (PPS), polyamideimide(PAI), or any other materials having similar properties to those listed.Table 1 below illustrates how these materials compare to PTFE in termsof tensile strength, compressive strength, and wear resistance. TABLE 1Tensile Compressive Wear Factor* Strength* Strength* “k” × 10⁻¹⁰Material (psi) (psi) (in.³-min/ft. lbs. hr) Nylon 6/6M 12500 12000 90Nylon 6 Cast 13000 15000 80 Acetal 10000 18000 30 PET-P 12000 12500 60PEEK 11000 26700 100 PPS 10900 18000 85 PAI 12000 22000 10 PTFE 35002000 600*Sample measurements based on industry accepted testing methods.

Referring to FIG. 3, the sealing element 38 extends in a plurality ofhelically wound convolutions 58 between first 54 and second 56 endsthereof. Thus, the sealing element 38 is in the shape of a cylindricalspiral. Referring back to FIG. 1, the flexible member 36 biases each ofthe plurality of convolutions 58 into sealing relation with the outerrunning surface 15 to provide the dynamic fluid seal.

The plurality of convolutions 58 comprise a continuous strand of thenon-PTFE material coiled or wrapped about the outer running surface 15.Each of the plurality of convolutions 58 are movable axially relative toone another such that the sealing element 38 can axially expand andcontract along the outer running surface 15 as the outer running surface15 rotates about the operational axis A. In the illustrations of FIGS. 3and 4, the sealing element 38 is shown expanded axially along the outerrunning surface 15.

In the preferred embodiment of FIG. 3, the sealing element 38 includestapered concentric rings 60, 62 that fully encircle the outer runningsurface 15 at each of the first 54 and second 56 ends. In thisembodiment, the sealing element 38 extends in the helical shape betweenthe concentric rings 60, 62. This yields a slinky-like shape for thesealing element 38. In an alternative embodiment of FIG. 4, theconcentric rings 60, 62 are removed and the entire sealing element 38extends in the helical shape between the ends 54, 56 to yield a woundcoil-like shape about the outer running surface 15.

Referring to FIG. 5, in another alternative embodiment of the sealingelement 38, the exterior surface 50 of the sealing element 38 defines anexterior groove 64 therein. The exterior groove 64 extends in a helicalshape between the first 54 and second 56 ends of the sealing element 38.Likewise, in a further alternative embodiment shown in FIG. 6, theradially inner annular sealing surface 52 of the sealing element 38defines a first interior groove 66 therein. The interior groove 66extends in a helical shape between the first 54 and second 56 ends ofthe sealing element 38. A second interior groove 70 is also defined inthe radially inner annular sealing surface 52 transverse to the firstinterior groove 66. The interior grooves 66, 70 are intended to providea hydrodynamic function to the sealing element 38 to further retain thefluid within the housing 12. Of course, additional grooves (not shown)or other hydrodynamic features (not shown) well known to those skilledin the art could be formed in the radially inner annular sealing surface52. While FIGS. 5 and 6 seemingly illustrate multiple exterior 64 andinterior 66, 70 grooves, it should be understood that multiple numeralshave been used for convenience and only one exterior groove 64 isactually illustrated in FIG. 5 and only one exterior groove 64 and twointerior grooves 66, 70 are actually illustrated in FIG. 6. This is dueto the helical nature of the grooves 64, 66, 70.

Referring to FIGS. 5A and 6A, a method of manufacturing the sealassembly 10 is also provided by the present invention. The methodincludes forming the exterior 64 and/or first interior 66 grooves of thesealing element 38 within a stock cylindrical piece 72 of the non-PTFEmaterial to define a helical fracture line 68 within the piece 72. Thegrooves 64, 66 can be molded or machined into the piece 72, given theproperties of the non-PTFE material. The flexible member 36 ispreferably molded or bonded onto the piece 72 after forming the grooves64 and/or 66. The flexible member 36 is then fixed by way of the annularlips 40, 42 onto the annular flange 22 of the rigid carrier 18.

Once the flexible member 36 and the piece 72 are secured to the rigidcarrier 18, the piece 72 is fractured along the fracture line 68 to formthe sealing element 38, as shown in FIGS. 5 and/or 6. This is preferablyaccomplished by forming the piece 72 with a slightly smaller diameterthan the outer running surface 15 such that as the piece 72 is fittedonto the outer running surface 15, the piece 72 fractures along thefracture line 68. Such a procedure may require special tooling. Inaddition, when fitted onto the outer running surface 15, the sealingelement 38 uncoils, i.e., the plurality of convolutions 58 are expandedabout the outer running surface 15. This uncoiling stretches the bondedflexible member 36 torsionally, thus providing an additional loadingfunction to the sealing relation between the sealing element 38 and theouter running surface 15. In effect, each of the plurality ofconvolutions 58 will operate independently in sealing against the outerrunning surface 15. The plurality of convolutions 58 provide ahydrodynamic effect which acts as a pump to redirect any fluid thatfinds its way under the seal back toward the interior (“oil side”) ofthe seal. The plurality of convolutions 58 can be single or multiplestart thread form, and can be uni or bi-directional, if desired.

Obviously, many modifications and variations of the present inventionare possible in light of the above teachings. The invention may bepracticed otherwise than as specifically described within the scope ofthe appended claims. It should also be appreciated that fragmentarycross-sectional views are utilized to illustrate the seal assembly 10 inaccordance with standard drawing convention. Hence, each component ofthe seal assembly 10 extends annularly about the outer running surface15 although not explicitly shown in the several views.

1. A seal assembly for providing a dynamic fluid seal between a housinghaving a bore and a shaft having an outer running surface rotatingwithin the bore about an operational axis relative to the housing, saidassembly comprising: a rigid carrier; a flexible member of elastomericmaterial mounted to said rigid carrier; and a sealing element fabricatedof non-polytetrafluoroethylene bearing grade plastic material having ahardness relatively greater than a hardness of said elastomericmaterial, said sealing element being retained by said flexible memberand having a radially inner annular sealing surface for moving with saidflexible member relative to said rigid carrier to seal about the outerrunning surface of the shaft.
 2. The assembly as set forth in claim 1wherein said sealing element extends in a plurality of helically woundconvolutions between first and second ends thereof such that each ofsaid plurality of convolutions are in sealing relation with the outerrunning surface of the shaft to provide the dynamic fluid seal.
 3. Theassembly as set forth in claim 2 wherein said plurality of convolutionscomprise a continuous strand of coiled non-polytetrafluoroethylenebearing grade plastic material.
 4. The assembly as set forth in claim 3wherein said sealing element includes tapered concentric rings at eachof said ends.
 5. The assembly as set forth in claim 2 wherein saidradially inner annular sealing surface defines a first interior groovetherein extending in a helical shape between said ends.
 6. The assemblyas set forth in claim 5 wherein said radially inner annular sealingsurface further defines a second interior groove therein extending in ahelical shape between said ends and transverse to said first interiorgroove.
 7. The assembly as set forth in claim 1 wherein said rigidcarrier includes an annular flange and said flexible member is furtherdefined as an annular hinge suspended from said annular flange andacting between said annular flange and said sealing element.
 8. Theassembly as set forth in claim 9 wherein said annular hinge includesfirst and second annular lips projecting radially outwardly therefromwith said annular lips defining a notch therebetween for receiving saidannular flange of said rigid carrier to sealably secure said annularhinge to said annular flange.
 9. The assembly as set forth in claim 10wherein said annular hinge includes a third lip projecting radiallyinwardly and abutting a first end of said sealing element to axiallyretain said first end of said sealing element.
 10. The assembly as setforth in claim 1 wherein said non-polytetrafluoroethylene bearing gradeplastic material is further defined as thermoplastic material having atensile strength greater than five thousand pounds per square inch and acompressive strength greater than five thousand pounds per square inch.11. The assembly as set forth in claim 10 wherein said thermoplasticmaterial has a wear factor of less than 200×10⁻¹⁰ in.³-min/ft.lbs.hr.12. The assembly as set forth in claim 10 wherein said thermoplasticmaterial includes any one of nylon, acetal, polyethylene terepthalate,polyetheretherketone, polyphenylene sulfide, and polyamideimide.
 13. Aseal assembly, comprising: a carrier; and a sealing element extending ina plurality of helically wound convolutions supported by said carrierfor sealing about an outer running surface of a rotating shaft toprovide a dynamic fluid seal therewith.
 14. The assembly as set forth inclaim 13 wherein said sealing element includes first and second ends andsaid plurality of convolutions comprise a continuous strand of coiledmaterial between said ends.
 15. The assembly as set forth in claim 14wherein said sealing element includes tapered concentric rings at eachof said first and second ends.
 16. The assembly as set forth in claim 13including a flexible member of elastomeric material mounted to saidcarrier for flexibly retaining said sealing element in sealing relationwith the outer running surface.
 17. The assembly as set forth in claim14 wherein said sealing element includes a radially inner annularsealing surface and said radially inner annular sealing surface definesa first interior groove therein extending in a helical shape betweensaid ends.
 18. The assembly as set forth in claim 17 wherein saidradially inner annular sealing surface further defines a second interiorgroove therein extending in a helical shape between said ends andtransverse to said first interior groove.
 19. The assembly as set forthin claim 18 wherein said carrier includes an annular flange and saidflexible member is further defined as an annular hinge suspended fromsaid annular flange and acting between said annular flange and saidsealing element.
 20. The assembly as set forth in claim 19 wherein saidannular hinge includes first and second annular lips projecting radiallyoutwardly therefrom with said annular lips defining a notch therebetweenfor receiving said annular flange of said carrier to sealably securesaid annular hinge to said annular flange.
 21. The assembly as set forthin claim 20 wherein said annular hinge includes a third lip projectingradially inwardly and abutting a first end of said sealing element toaxially retain said first end of said sealing element.
 22. The assemblyas set forth in claim 13 wherein said sealing element is formed from anon-polytetrafluoroethylene bearing grade plastic material.
 23. Theassembly as set forth in claim 22 wherein saidnon-polytetrafluoroethylene bearing grade plastic material is furtherdefined as thermoplastic material having a tensile strength greater thanfive thousand pounds per square inch and a compressive strength greaterthan five thousand pounds per square inch.
 24. The assembly as set forthin claim 23 wherein said thermoplastic material has a wear factor ofless than 200×10⁻¹⁰ in.³-min/ft.lbs.hr.
 25. The assembly as set forth inclaim 23 wherein said thermoplastic material includes any one of nylon,acetal, polyethylene terepthalate, polyetheretherketone, polyphenylenesulfide, and polyamideimide.
 26. A shaft seal system, comprising: ahousing formed with a bore having a generally cylindrical wall and anannular shoulder disposed transverse to said wall; a shaft having anouter running surface disposed about an operational axis within saidbore; and a seal assembly disposed about said shaft and having a rigidcarrier, a flexible member of elastomeric material mounted to said rigidcarrier, and a radially acting sealing element flexibly retained by saidflexible member in sealing relation with said outer running surface ofsaid shaft, said sealing element being formed from anon-polytetrafluoroethylene bearing grade plastic material having ahardness relatively greater than said elastomeric material with saidsealing element extending in a plurality of helically wound convolutionsabout said outer running surface.
 27. The assembly as set forth in claim26 wherein said sealing element includes a radially inner annularsealing surface facing said outer running surface and said radiallyinner annular sealing surface defines a first interior groove thereinextending in a helical shape about said outer running surface.
 28. Theassembly as set forth in claim 27 wherein said radially inner annularsealing surface further defines a second interior groove thereinextending in a helical shape about said outer running surface andtransverse to said first interior groove.
 29. The assembly as set forthin claim 26 wherein said rigid carrier includes an annular flange andsaid flexible member is further defined as an annular hinge suspendedfrom said annular flange and acting between said annular flange and saidsealing element to bias each of said plurality of convolutions insealing relation with said outer running surface.
 30. The assembly asset forth in claim 29 wherein said annular hinge includes first andsecond annular lips projecting radially outwardly therefrom with saidannular lips defining a notch therebetween for receiving said annularflange of said rigid carrier to sealably secure said annular hinge tosaid annular flange.
 31. The assembly as set forth in claim 30 whereinsaid annular hinge includes a third lip projecting radially inwardly andabutting a first end of said sealing element to axially retain saidfirst end of said sealing element.
 32. A method of manufacturing a sealassembly having a rigid carrier, a flexible member of elastomericmaterial mounted to the rigid carrier, and a sealing element retained bythe flexible member and formed from a stock piece of sealing material toprovide a dynamic fluid seal between a housing having a bore and a shafthaving an outer running surface rotating within the bore about anoperational axis relative to the housing, said method comprising thesteps of: forming a groove extending helically within a surface of thestock piece of sealing material to define a fracture line within thestock piece of sealing material; and fracturing the stock piece ofsealing material along the fracture line after the groove is formed toform the sealing element with a plurality of helically woundconvolutions for sealing about the outer running surface of the shaft toprovide the dynamic fluid seal.
 33. The method as set forth in claim 32including molding the flexible member onto the stock piece of sealingmaterial after forming the groove.
 34. The method as set forth in claim33 including securing the flexible member to the rigid carrier after theflexible member is molded onto the stock piece of sealing material. 35.The method as set forth in claim 32 wherein forming the groove extendinghelically within the surface of the stock piece of sealing material isfurther defined as molding the groove extending helically within thesurface.
 36. The method as set forth in claim 35 including molding agroove extending helically on a second surface of the stock piece ofsealing material opposite the other surface to further define thefracture line.
 37. The method as set forth in claim 32 wherein formingthe groove extending helically within the surface of the stock piece ofsealing material is further defined as machining the groove extendinghelically within the surface.
 38. The method as set forth in claim 37including machining a groove extending helically on a second surface ofthe stock piece of sealing material opposite the other surface tofurther define the fracture line.